1. Field of the Invention
The present invention relates to a step-up DC-DC converter, and particularly, to a step-up DC-DC converter that synchronizes control operations of a first switching element and a second switching element, and supplies power at an input side to an output side.
2. Description of the Related Art
A frequently used method for a power device to convert an input voltage to a specified output voltage includes power conversion at high efficiency by using a switching DC-DC converter.
The switching DC-DC converter controls a first switching element in synchronization with a second switching element, and this allows formation of channels in the switching elements, and thus, resistance of the switching elements in an ON state can be decreased, and high efficiency power conversion can be performed even under a heavy load. However, although high power conversion efficiency can be obtained under a heavy load, a charging and discharging current occurring when the second switching element switches under a light load becomes non-negligible, so that the overall conversion efficiency lowers.
For example, Japanese Laid Open Patent Application No. 2001-197727 (hereinafter, referred to as “reference 1”) discloses a method able to control a first switching element in synchronization with a second switching element, thus reduce resistance of the switching elements in an ON state, and obtain high efficiency power conversion even under a heavy load.
However, in the method disclosed in reference 1, although high efficiency power conversion can be obtained under a heavy load, since the first switching element and the second switching element are both switched on under a light load, while switching element resistance inside a circuit can be reduced, current consumption for charging and discharging the switching element becomes non-negligible, and it is difficult to obtain high efficiency power conversion under a light load.